{"id":22511,"date":"2024-01-11T14:44:56","date_gmt":"2024-01-11T12:44:56","guid":{"rendered":"https:\/\/fractory.com\/?p=22511"},"modified":"2024-02-20T18:14:35","modified_gmt":"2024-02-20T16:14:35","slug":"shot-peening-explained","status":"publish","type":"post","link":"https:\/\/fractory.com\/shot-peening-explained\/","title":{"rendered":"Shot Peening Explained – Definiton, Process & More"},"content":{"rendered":"

Shot peening is a cold working process that alters the mechanical properties<\/a> on the metal’s surface and creates a compressive residual stress layer. Its primary purpose is to prevent the spread of microcracks on a surface. Shot peening also improves a material’s fatigue resistance, strength, and durability, making it effective in increasing its service life.<\/p>\n

Shot Peening Process<\/h2>\n

Shot peening is a cold working process that subjects the material’s surface to plastic deformation using peening media. The process uses shot media that generally comes in the form of steel, ceramic, or glass beads. This media is bombarded onto the part’s surface at high velocities, generating enough force to compress the surface and create small indentations. It converts the residual tensile stress into beneficial residual compressive stress which improves the material’s strength under load.<\/p>\n

The application of the shot media may either be delivered using compressed air or a wheel turbine. The principle of shot peening remains the same with both types of equipment. Factors such as coverage, intensity, angle, and shot quality have a way higher impact on converting tensile stresses to compressive residual stress than the chosen process type.<\/p>\n

Each shot particle hits the component’s surface at around 30 to 100 m\/s, encasing the layer with residual compressive stresses. Plastic deformation<\/a>, enabled by shot peening can also correct the surface roughness of a workpiece. Thousands of indentations compress and strengthen the metal, making it more resistant to failure. A correctly shot peened component will last longer and have higher maximum load capacities. Too much peening may induce excessive cold working though, which can lead to fatigue cracks and lower fatigue strength<\/a> in return.<\/p>\n

An Almen Strip Test<\/strong> can be performed throughout the shot peening process to measure the intensity of each shot particle. This test uses a flat strip bombarded by a shot stream which is usually adjusted through a shot flow controller. An Almen Gauge measures the bentness of the strip which determines the intensity.<\/p>\n

Separators<\/strong> are used for the recovery of used media and removal of shot fragments. Feeders<\/strong> replace the number of damaged media for operation.<\/p>\n

Other uses of this process include shot peening forming,<\/strong> a method in which the component is slightly bent from the force applied. It may be used for thin panels, skins, and wing flaps. Shot peening may also be used for correction of distortion<\/strong> which aims to flatten surfaces (opposite of forming).<\/p>\n

Portable shot peening or flap peening is used for extremely difficult areas or repairs (mostly aircraft). It consists of a kevlar matrix with a flap of balls that are propelled pneumatically or electrically to the targeted area.<\/p>\n

Shot Peening Media<\/h3>\n

\"Close<\/p>\n

There are various forms of shot peening media used to generate compressive stress on the material surface. Each has its own HRC (Hardness Rockwell C Scale) value which impacts the amount of force applied to the surface.<\/p>\n

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  1. \n

    Cast steel shots<\/strong> (40 ~ 50 HRC) are round metallic in shape and are made from steel scrap and alloys which are melted at ~1650\u00b0C (3000\u00b0F). Quenching<\/a>, tempering<\/a>, and other heat treatments are used to manufacture these steel shots to achieve the desired hardness. Cast steel shots are suitable for most peening intensities of ferrous and non-ferrous metal components. The major downside of a cast shot is the fact that it may shatter into sharp steel fragments at high speeds\/forces, damaging the component.<\/p>\n<\/li>\n

  2. \n

    Ceramic shots<\/strong> (57 ~ 63 HRC) are pills made from approximately 67% zirconium dioxide, 31% silica, and 2% aluminium oxide. They have an extremely high density and hardness which makes it optimal for increasing the surface hardness<\/a> of non-ferrous metals such as alloys of aluminium and titanium.<\/p>\n<\/li>\n

  3. \n

    Glass beads<\/strong> (>40 HRC) are made from soda lime which can come from scrap glass. The glass is crushed, melted, and formed into spheres. Glass beads are primarily used for aluminium, magnesium, titanium, and other ferrous metals. Peening with glass beads may be used as a secondary process to steel shot peening to remove iron from the surface and improve the part’s smoothness<\/a>.<\/p>\n<\/li>\n

  4. \n

    Cut wire shots <\/strong>(50 ~ 60 HRC) are cylindrical with rounded edges and are homogenous in their composition. A cut wire shot is obtained from a cutting wire that is divided into equal lengths relative to its wire diameter. This type of shot peening media is quite popular due to its low surface contamination, solid and uniform hardness, and no dust generated. It is used for ferrous and nonferrous<\/a> applications but is ruled out when small-sized shots are needed. It leaves a consistent peening intensity on the surface and is unbreakable, unlike other media. Cut wire shots may come in the form of aluminium, carbon steel, copper, stainless steel, and zinc.<\/p>\n<\/li>\n<\/ol>\n

    Shot Media Considerations<\/h4>\n

    There are quite a few variables to consider when selecting shot media aside from its type. These considerations are done in comparison to the properties of the workpiece and its desired outcome.<\/p>\n